Signal Iduna Park was rocking for the contest and BVB duly obliged their partisan home support by storming into the lead early on. Robert Lewandowski scored all four of the home side's goals, while Cristiano Ronaldo claimed a solitary strike for the visitors.

Let's break down this exciting affair tactically.

Formations

With Angel Di Maria arriving late in Dortmund, Jose Mourinho felt forced into changing his lineup. Luka Modric came into the side as Real Madrid adopted a strange 4-3-3-esque blend, forcing Mesut Oezil to the wide areas.

Dortmund went with their typical 4-2-3-1 formation, Mario Goetze played as a No. 10 and the impressive Marco Reus was a key central winger from the left.

Dortmund on top

Right from the word go, Dortmund found room to play. Look at the image above and you can see why—the odd formation change allowed playmaker Ilkay Gundogan to do whatever he wanted.

He stayed deep—very deep, to start with—and dictated the game's tempo, seeking out Reus and Goetze at every chance and helping BVB take hold of the tie.

Ilkay played very well and remained instrumental to the attack, but unlike Malaga, who put Duda on him to try and reduce his influence on the game, Madrid simply let him play.

The lack of a No. 10 hurt los Merengues here, as no one was close to close him down.

Mats Hummels was also left free to stride forward and play positive passes, and the lack of pressure on Juergen Klopp's deep-lying playmakers caused Madrid problems all night.

Madrid's struggle

As mentioned, Modric joined Sami Khedira and Xabi Alonso in a three-man midfield, and the distinct lack of a No. 10 affected them: Not only did Gundogan get time on the ball, but los Blancos found it rather difficult to hold the ball in forward areas for prolonged periods.

Sven Bender—an excellent run-tracker—filtered back to sit beside Gundogan in a pivot, but they were rarely challenged head on by a playmaker.

Alonso was the deepest of the three central players, and his lack of pace was exposed several times by a roaming, marauding Reus. Goetze applied plenty of pressure to him when on the ball, forcing the Spaniard to drop deeper and deeper until he was level with his centre-backs.

Whenever the Madrid midfield shifted forward, BVB's lightning-fast counterattacks were launched and Reus was able to meander into the space behind Khedira and rinse Alonso for pace.

Fabio Coentrao found it tough to get involved for the first 25 minutes, too—Jakub Blaszsykowski did a fine job tracking and blocking him, while a lack of possession gave him very few chances to overlap.

Lukasz Piszczek largely contained Ronaldo single-handedly, and it was only a whirlwind minute that saw the Portuguese get on the scoresheet. Neven Subotic bossed the aerial tussle, Piszczek matched him on the ground.

Changes?

Mourinho did absolutely nothing to block Gundogan's influence on the game, making late changes to switch to a 4-2-4 formation that still committed little to the midfield battle.

Karim Benzema joined Ronaldo up front, Oezil remained wide and Di Maria came onto the left flank. Khedira and Alonso became a proper holding pivot, but Dortmund had it pretty easy on the ball.

Physically, BVB were superb. They pressed, harried, fought and committed in every single second of the game, giving only Raphael Varane and Pepe time on the ball.

Lewandowski and Gundogan will take the plaudits, and not to take anything away from the latter's stellar performance, but Madrid simply lay down in front of him.

Conclusion

Dortmund have one foot in the final and deservedly so—Goetze leaving or not, the team was up for it and the crowd was superb.

It was a real shock to see Mourinho do nothing to stop Gundogan killing his side—even something as simple as shifting Modric forward to pressurise him was not done—and he's paid the price.

Reus enjoyed space between the lines and bullied a slow Alonso, with the collision between the two resulting in a penalty the very epitome of the mismatched contest.

What's ironic is that Mou did everything he could to mask the lack of mobility in Alonso from a playmaking perspective, but instead the Spaniard was burned on the defensive side of the game.